1. Field of the Invention
This invention relates to a thin type DC brushless motor or synchronous motor.
2. Description of the Prior Art
In general, regarding apparatus for use in the fields of electrical communications, business transactions, measurements, and the like, it is being aggressively attempted to improve components from the aspects of the materials used and structures thereof so as to render the entire apparatus smaller in size, lighter in weight and lower in power consumption. Accordingly, similar requirements are indispensable for electric motors which are employed in these type of apparatus. In order to meet such requirements, one of the inventors of the present application has previously developed a compact capacitor motor which is, not only miniaturized, but also thin in thickness, exhibits a high degree of performance including a large shaft output, and for which a patent application has been filed. The structure of the compact capacitor motor is as disclosed in the official gazette of Japanese Patent Applications Laid-open No. 57-91658 (corresponding to U.S. Pat. No. 4,514,655), and will be outlined with reference to FIGS. 15 and 16 of the accompanying drawings.
As shown in the half-sectional side view of FIG. 15, the prior-art compact capacitor motor comprises a frame 101, a stator core 102 which is press-fitted in the frame 101 and which is fixed to the frame 101 by bonding and/or caulking, and a rotor 103 which is arranged in the hollow central portion of the stator core 102 so as to be disposed concentrically therewith. FIG. 16 is an exploded perspective view which shows only the stator core 102 and the rotor 103 of the motor in FIG. 15. The rotor 103 is composed of a rotor core 103A, aluminum bars 103B, aluminum end rings 103C and rotary shaft 103D. As shown in FIG. 15, this rotor 103 is rotatably supported on a sleeve 105 with which the frame 101 is provided, through means of a ball bearing or an oilless metal component 104 associated with the rotary shaft 103D. As clearly shown in FIG. 16, the stator core 102 is so constructed so as to include a ring-shaped core portion 102A which surrounds the core 103A of the rotor 103 and which has a thickness substantially equal to the axial thickness of rotor core 103A, and four coil winding core portions 102B which extend radially outwardly from the outer periphery of the ring-shaped core portion 102A, which have a thickness less than the thickness of the ring-shaped core portion 102A and which serve to mount or support stator coils 106 thereon (refer to FIG. 15). According to the structure of this motor, the thickness of the coil winding core portions 102B of the stator core 102 is less than that of the ring-shaped core portion 102A, so that the outer thickness of the stator coils 106 to be disposed thereon can be reduced to a corresponding extent, and the thinness of the motor itself can be achieved.
A thinned geometry and an enhanced performance are also required of a DC brushless motor. The inventors made studies on adopting the structure of the motor as stated above, especially the structure of the stator core thereof for the DC bruchless motor, so as to there-by achieve the thinned geometry and the enhanced performance. It has been revealed, however, that when the structure of the stator core of the motor as stated before is applied to the DC brushless motor, enhancement in performance cannot be appreciably accomplished though thinning in geometry is possible.